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Newswise — LEXINGTON, Ky. (April 21, 2014) -- A group of scientists from the University of Kentucky College of Medicine and the Sanders-Brown Center on Aging has found interesting new information in a study on depression and neuropsychological function in Parkinson's disease (PD).

Published in the journal Psychiatry Research, the study, which assessed cognitive function in depressed and non-depressed patients with PD, found that the dopamine replacement therapy commonly used to treat motor symptoms of Parkinson's disease was associated with a decline in cognitive performance among depressed Parkinson patients. In contrast, non-depressed Parkinson patients’ cognitive function improved on dopamine replacement therapy.

The study also found that mood in depressed Parkinson's patients was actually worse while on dopaminergic medications.

"This was a surprise," said Lee Blonder, Ph.D., the study's principal investigator. "It is the opposite of our original hypothesis that both groups of PD patients would improve in cognitive performance on dopaminergic medications, and that mood in the depressed PD group would also improve."

A cohort of 28 patients with PD -- 18 nondepressed and 10 depressed -- were given a baseline series of tests to assess cognitive function and the incidence and severity of depression. They were then re-tested with and without their dopamine replacement therapy.Results revealed a statistically signiﬁcant interaction between depression and medication status on three measures of verbal memory and a facial affect naming task. In all cases, depressed Parkinson's patients performed signiﬁcantly more poorly while on dopaminergic medication than while off. The opposite pattern emerged for the non-depressed Parkinson's group.

Depression is a common and serious co-morbidity in patients with Parkinson's; studies suggest that approximately 40 percent of PD patients suffer from depression.

Blonder cautions that these results are to some extent preliminary due to the small cohort of 28 participants. “Additional studies are required before these results should be used to alter treatment plans," Blonder says. But, "future research should ultimately focus on investigating treatment options for patients with Parkinson’s and depression to maximize patient function without compromising their mental health.”

Psychiatry Research is a peer-reviewed journal that includes coverage of clinically related basic studies in the fields of neuropharmacology, neurochemistry, neuroendocrinology, electrophysiology, psychology, genetics, and brain imaging.